关键词: ¹⁴C, 核反应堆冷却水, 液闪测量, 乙醇胺, TritonX－100

Abstract: For determining the trace ¹⁴C in nuclear reactor coolingwater, two methods based on sorption of ¹⁴CO₂ in a solution and subsequent liquit scintillation (LS) counting of the ¹⁴C were developed. Initially, a water sample was acidified by H₂SO₄ and distilled in a distillator to produce ¹⁴CO₂ gas which was converted from CO^2-₃ anion in the water. In the first method of Ca¹⁴CO₃ formation, ¹⁴CO₂ gas was collected as Ca¹⁴CO₃ precipitate by NaOH and CaCl₂ solution, and then Ca¹⁴CO₃ was dispersed in a colloidal liquid scintillator (toluene : TritonX-100 : water = 2 : 1 : 1.5) for LS counting. The sorption yield was >90%. The detection limit of this sorption in Ca¹⁴CO₃-LS method was 3.3×10^-10g/L. In the method of sorption by organic alkali, ¹⁴CO₂ gas was absorbed by an ethanolamine cocktail(PPO 6g, POPOP 0.2g, ethanolamine 120mL, ethylene glycol monomethyl ether 400mL, toluene 480mL) which can be directly counted in a LS counter. The sorption yield was also >90%, and the detection range of ¹⁴C concentration was wider, and the detection limit was improvedto 3.3×10^-11g/L, lower than the previous one order of magnitude. By taking the second method, cooling water samples from two nuclear reactors were assayed. ¹⁴C content of the samples taken from a reactor of the Chinese Institute of Nuclear. Energy was determined as 5.0×10^-11g/L. In the same samples 6 other trace radionuclides (⁵⁸Co, ⁴⁶Sc, ⁵⁴Mn, ^110mAg, ⁶⁰Co and ⁵¹Cr),ranging from 0.40 to 30.0 Bq/L in specific activity, were also detected by γ-ray spectrum measurement. Whereas, no radioactivity was detected in another reactor water sample.

Key words: ¹⁴C, nuclear reactor cooling water, liquid scintillation counting, etha-nolamine, Triton X-100